local function divide_string( str, max, fillChar )
    fillChar = fillChar or ""
    local result = {}
 
    local start = 1
    for i = 1, #str do
       if i % max == 0 then
          table.insert( result, str:sub( start, i ) )
          start = i + 1
       elseif i == #str then
          table.insert( result, str:sub( start, i ) )
       end
    end
 
    return result
 end
 
 local function number_to_bit( num, length )
    local bits = {}
 
    while num > 0 do
       local rest = math.floor( math.fmod( num, 2 ) )
       table.insert( bits, rest )
       num = ( num - rest ) / 2
    end
 
    while #bits < length do
       table.insert( bits, "0" )
    end
 
    return string.reverse( table.concat( bits ) )
 end
 
 local function ignore_set( str, set )
    if set then
       str = str:gsub( "["..set.."]", "" )
    end
    return str
 end
 
 local function pure_from_bit( str )
    return ( str:gsub( '........', function ( cc )
                return string.char( tonumber( cc, 2 ) )
             end ) )
 end
 
 local function unexpected_char_error( str, pos )
    local c = string.sub( str, pos, pos )
    return string.format( "unexpected character at position %d: '%s'", pos, c )
 end
 
 --------------------------------------------------------------------------------
 
 local basexx = {}
 
 --------------------------------------------------------------------------------
 -- base2(bitfield) decode and encode function
 --------------------------------------------------------------------------------
 
 local bitMap = { o = "0", i = "1", l = "1" }
 
 function basexx.from_bit( str, ignore )
    str = ignore_set( str, ignore )
    str = string.lower( str )
    str = str:gsub( '[ilo]', function( c ) return bitMap[ c ] end )
    local pos = string.find( str, "[^01]" )
    if pos then return nil, unexpected_char_error( str, pos ) end
 
    return pure_from_bit( str )
 end
 
 function basexx.to_bit( str )
    return ( str:gsub( '.', function ( c )
                local byte = string.byte( c )
                local bits = {}
                for i = 1,8 do
                   table.insert( bits, byte % 2 )
                   byte = math.floor( byte / 2 )
                end
                return table.concat( bits ):reverse()
             end ) )
 end
 
 --------------------------------------------------------------------------------
 -- base16(hex) decode and encode function
 --------------------------------------------------------------------------------
 
 function basexx.from_hex( str, ignore )
    str = ignore_set( str, ignore )
    local pos = string.find( str, "[^%x]" )
    if pos then return nil, unexpected_char_error( str, pos ) end
 
    return ( str:gsub( '..', function ( cc )
                return string.char( tonumber( cc, 16 ) )
             end ) )
 end
 
 function basexx.to_hex( str )
    return ( str:gsub( '.', function ( c )
                return string.format('%02X', string.byte( c ) )
             end ) )
 end
 
 --------------------------------------------------------------------------------
 -- generic function to decode and encode base32/base64
 --------------------------------------------------------------------------------
 
 local function from_basexx( str, alphabet, bits )
    local result = {}
    for i = 1, #str do
       local c = string.sub( str, i, i )
       if c ~= '=' then
          local index = string.find( alphabet, c, 1, true )
          if not index then
             return nil, unexpected_char_error( str, i )
          end
          table.insert( result, number_to_bit( index - 1, bits ) )
       end
    end
 
    local value = table.concat( result )
    local pad = #value % 8
    return pure_from_bit( string.sub( value, 1, #value - pad ) )
 end
 
 local function to_basexx( str, alphabet, bits, pad )
    local bitString = basexx.to_bit( str )
 
    local chunks = divide_string( bitString, bits )
    local result = {}
    for key,value in ipairs( chunks ) do
       if ( #value < bits ) then
          value = value .. string.rep( '0', bits - #value )
       end
       local pos = tonumber( value, 2 ) + 1
       table.insert( result, alphabet:sub( pos, pos ) )
    end
 
    table.insert( result, pad )
    return table.concat( result )   
 end
 
 --------------------------------------------------------------------------------
 -- rfc 3548: http://www.rfc-editor.org/rfc/rfc3548.txt
 --------------------------------------------------------------------------------
 
 local base32Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"
 local base32PadMap = { "", "======", "====", "===", "=" }
 
 function basexx.from_base32( str, ignore )
    str = ignore_set( str, ignore )
    return from_basexx( string.upper( str ), base32Alphabet, 5 )
 end
 
 function basexx.to_base32( str )
    return to_basexx( str, base32Alphabet, 5, base32PadMap[ #str % 5 + 1 ] )
 end
 
 --------------------------------------------------------------------------------
 -- crockford: http://www.crockford.com/wrmg/base32.html
 --------------------------------------------------------------------------------
 
 local crockfordAlphabet = "0123456789ABCDEFGHJKMNPQRSTVWXYZ"
 local crockfordMap = { O = "0", I = "1", L = "1" }
 
 function basexx.from_crockford( str, ignore )
    str = ignore_set( str, ignore )
    str = string.upper( str )
    str = str:gsub( '[ILOU]', function( c ) return crockfordMap[ c ] end )
    return from_basexx( str, crockfordAlphabet, 5 )
 end
 
 function basexx.to_crockford( str )
    return to_basexx( str, crockfordAlphabet, 5, "" )
 end
 
 --------------------------------------------------------------------------------
 -- base64 decode and encode function
 --------------------------------------------------------------------------------
 
 local base64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"..
                        "abcdefghijklmnopqrstuvwxyz"..
                        "0123456789+/"
 local base64PadMap = { "", "==", "=" }
  
 function basexx.from_base64( str, ignore )
    str = ignore_set( str, ignore )
    return from_basexx( str, base64Alphabet, 6 )
 end
 
 function basexx.to_base64( str )
    return to_basexx( str, base64Alphabet, 6, base64PadMap[ #str % 3 + 1 ] )
 end
 
 --------------------------------------------------------------------------------
 -- URL safe base64 decode and encode function
 --------------------------------------------------------------------------------
 
 local url64Alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"..
                       "abcdefghijklmnopqrstuvwxyz"..
                       "0123456789-_"
  
 function basexx.from_url64( str, ignore )
    str = ignore_set( str, ignore )
    return from_basexx( str, url64Alphabet, 6 )
 end
 
 function basexx.to_url64( str )
    return to_basexx( str, url64Alphabet, 6, "" )
 end
 
 --------------------------------------------------------------------------------
 --
 --------------------------------------------------------------------------------
 
 local function length_error( len, d )
    return string.format( "invalid length: %d - must be a multiple of %d", len, d )
 end
 
 local z85Decoder = { 0x00, 0x44, 0x00, 0x54, 0x53, 0x52, 0x48, 0x00,
                      0x4B, 0x4C, 0x46, 0x41, 0x00, 0x3F, 0x3E, 0x45, 
                      0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 
                      0x08, 0x09, 0x40, 0x00, 0x49, 0x42, 0x4A, 0x47, 
                      0x51, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 
                      0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 
                      0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 
                      0x3B, 0x3C, 0x3D, 0x4D, 0x00, 0x4E, 0x43, 0x00, 
                      0x00, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 
                      0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 
                      0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 
                      0x21, 0x22, 0x23, 0x4F, 0x00, 0x50, 0x00, 0x00 }
 
 function basexx.from_z85( str, ignore )
    str = ignore_set( str, ignore )
    if ( #str % 5 ) ~= 0 then
       return nil, length_error( #str, 5 )
    end
 
    local result = {}
 
    local value = 0
    for i = 1, #str do
       local index = string.byte( str, i ) - 31
       if index < 1 or index >= #z85Decoder then
          return nil, unexpected_char_error( str, i )
       end
       value = ( value * 85 ) + z85Decoder[ index ]
       if ( i % 5 ) == 0 then
          local divisor = 256 * 256 * 256
          while divisor ~= 0 do
             local b = math.floor( value / divisor ) % 256
             table.insert( result, string.char( b ) )
             divisor = math.floor( divisor / 256 )
          end
          value = 0
       end
    end
 
    return table.concat( result )
 end
 
 local z85Encoder = "0123456789"..
                    "abcdefghijklmnopqrstuvwxyz"..
                    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"..
                    ".-:+=^!/*?&<>()[]{}@%$#"
 
 function basexx.to_z85( str )
    if ( #str % 4 ) ~= 0 then
       return nil, length_error( #str, 4 )
    end
 
    local result = {}
 
    local value = 0
    for i = 1, #str do
       local b = string.byte( str, i )
       value = ( value * 256 ) + b
       if ( i % 4 ) == 0 then
          local divisor = 85 * 85 * 85 * 85
          while divisor ~= 0 do
             local index = ( math.floor( value / divisor ) % 85 ) + 1
             table.insert( result, z85Encoder:sub( index, index ) )
             divisor = math.floor( divisor / 85 )
          end
          value = 0
       end
    end
 
    return table.concat( result )
 end
 
 return basexx